Skirt for an air cushion vehicle and filament member thereto

ABSTRACT

The air cushion chambers of an air cushion vehicle are horizontally delimited by a skirt. The skirt comprises brushes with elongated downwards extended filaments (9), which have downwards diminishing cross-sectional area thereby providing the brushes with sufficient stiffness to maintain the pressure in the air cushion chamber and such a large flexibility in the lower section of the skirt that ice can hardly deposit thereon. The filament members are mounted in a guide profile (2) in such a manner that above the members there is a chamber (12) for dispersion and conveying of deicing fluid which form the chamber (12) via a flow passage in every filament member may pass down into a clearspace (10) between the filaments (9). At least one of the filaments (109) has forward protruding web (115) on one of its sides and a backwards protruding web (116) on its other side. When mounted, the webs of the filaments may seize each other when the skirt is transversely deflected and thereby the webs lock the individual brush members to one another which provides the skirt with a larger stiffness in the transverse direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to filament member for a skirt for an air cushionvehicle which has beneath the bottom of the vehicle hull a number of aircushion chambers which are delimited in horizontal direction by theskirt and into which air supply means may blow air for maintaining theair cushion in the air cushion chamber during operation of the vehicle,the skirt including elongated, downwards extending filaments.

2. Description of the Prior Art

A skirt for an air cushion vehicle is known from the U.S. Pat. Nos.3,249,167 and 3,172,494 showing skirts with brushes in the form of rods,wires, cords, chains or filaments made of plastic.

Another skirt is known from SE-B-305812, where skirt members are hangingdown from the hull. The flexible skirt members are shaped with largecross-sections merging into each other such as triangular cross-sectionswith the apex facing alternatively inwards and outwards. These skirtmembers are not of the filament type.

The skirt extends along the periphery of the air cushion chambers andserves to prevent the air from freely escaping the chambers. In thetraditional air cushion vehicles the skirt is constructed from acontinuous rubber sheet, but such a sheet is frequently exposed todamage when the air cushion vehicle crosses obstacles which may seizethe skirt.

A skirt of brushes as known from the above U.S.A.-patents possess theadvantage that obstacles may pass freely through the brushes withoutdamaging these.

It is a well known problem of air cushion vehicles that they hardly canbe used in waters where there is risk of icing up because the ice iseasily formed on the skirt and impedes the correct functioning thereof.This problem is especially distinct by the brushformed skirts having avery large surface area compared to the length of the skirt. As aircushion vehicles are very sensitive to weight changes even smallerdeposits of ice on the skirt may demand suspension of the vehicleoperation.

The object of the invention is to provide a skirt more appropriate fornavigation in cold waters.

With this aim the filament member according to the invention ischaracterized in that the filament member has an upper base portion withengagement means for the attachment of the member to a retainer, andthat the member includes several juxtaposed elongated filamentsextending from the base portion and having less cross-sectional area atthe free end of the filaments than at the root thereof. Such a membermay in a simple manner be manufactured from a plastics material by meansof injection moulding and it provides for assembling a skirt having anydesired length simply by placing in the retainer a number of memberscorresponding to the desired skirt length. As each member only comprisescomparatively few filaments such a skirt is repairable at low-costs inthe event of skirt damages, because only the damaged members are to bereplaced.

SUMMARY OF INVENTION

By designing the filaments with less cross sectional area at their lowerends, that are most frequently in contact with the water andconsequently especially exposed to icing, they are here substantiallymore flexible than at their upper ends. The larger flexibility resultsin larger deflections and more rapid movements in the lower section ofthe skirt, thereby enabling any deposited ice to loosen and fall off theskirt. The larger cross-sectional area in the upper part of thefilaments ensures that the skirt preserves sufficient stiffness in orderto keep the air inside the air cushion chamber. The embodiment accordingto the invention thus gives due consideration to the conflictingconsiderations that the skirt must have the sufficient stiffness toconfine the air, but also a flexibility to prevent icing. With the viewof further preventing ice formations on a skirt the filament member isadvantageously designed so that at the base portion there is at leastone flow passage which may set at least one interspace between thefilaments in flow communication with a chamber for conveying de-icingfluid. The de-icing fluid may be a hot gas, e.g. extracted hotcompartment air from the cabin of the vehicle or exhaust gas from themain engine of the vehicle. A ventilator may press the hot gas into thechamber wherefrom the gas via the flow passage will be conveyed downbetween the filaments and heat these thereby counteracting iceformations. The de-icing fluid may alternatively be a proper de-icingagent, like propyl alcohol, which by a pump is injected into thechamber, wherefrom it can flow through the flow passage and downwardsover the filaments and prevent ice formations.

In a preferred embodiment the thickness of the filament member in thelongitudinal direction of the skirt is substantially even over theentire length of the member, whereas the width of the filaments of themember, in the transverse direction of the skirt, diminishes towards thetip of the filaments. When the members are assembled to a complete skirtthe by and large even thickness of the members in the length directionof the skirt has as a consequence that filaments abut against each otherto form a surface which in its undeformed condition is continuous andprovides an effective barrier to the air in the air cushion. Thediminishing width of the filaments in the transverse direction ensuresthe large flexibility in the transverse direction of the skirt aimed atfor the removal of ice.

In an especially simple embodiment the retainer is a guide profile witha downwards facing opening for receiving the filament members, and theprofile and the engagement means on the members are designed so that inthe profile above the assembled members there is a chamber extending inthe longitudinal direction of the profile and serving for dispersion andconveying of de-icing fluid. By designing the chamber as an integralpart of the retainer the number of structural parts of the skirt areminimized and consequently, the skirt can be manufactured at low costs.The guide profile may further be made in a standard length which canreceive a certain number of filament members thus permitting an easy andrapid renewal of skirt sections.

According to the invention it is also possible to design the filamentmember so that the skirt gets larger resultant transversal stiffness,namely by the filament member being characterized in that at least oneof the juxtaposed elongated filaments has a web that protrudes in thelongitudinal direction of the skirt and is intended to project over partof the adjacent filament member.

The projecting web has the effect that the individual filament membersin the skirt to some extent are connected thereby preventing a separatedeflection of an individual filament member, because a transverselydeflecting filament pulls the adjacent filaments into its deflectionmovement.

In a preferable, simple embodiment the filament with the web is Z-shapedin sectional view and has, when mounted, a forwards extending web on oneside of the filament and a backwards extending web on its other side.When the filaments are mounted in the retainer the forwards projectingweb of one member is situated opposite the backwards facing web of theadjacent member, so that the two mentioned webs will seize each other,if the member is deflected in the transverse direction of the skirt. Dueto the fact that the body portion of the Z-shape extends in thetransverse direction of the skirt the filament member further obtains acomparatively large stiffness in this direction thereby allowing, withonly a small number of filaments in the transverse direction of theskirt, maintenance of adequately high positive pressure in the aircushion chambers delimited by the skirt.

The filament member may include at least three filaments of which twoouter filaments have substantially larger dimension in the transversedirection of the skirt than a central filament. The two outer relativelystiff filaments provide the skirt with the desired stiffness againstbending, while the central filament has larger flexibility and iscapable of rapidly adjusting to local pressure variations across theskirt and thus form an effective air barrier.

This embodiment may be further detailed so that the two outer filamentshave a Z-shaped cross-section and the central filament has across-section being elongated in the longitudinal direction of theskirt. The central filaments bear against each other and form awall-like air barrier and they are kept in position by the substantiallymore rigid outer filaments, which due to the Z-shape ensure an effectiveinter locking of the individual filament members.

The invention further relates to a skirt being composed of a largenumber of the above filament members.

The invention will now be described in detail with reference to theschematical drawings, in which

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 in a sectional perspective view shows a skirt section mounted atthe bottom of the vehicle hull,

FIG. 2 shows an individual filament member according to the invention,in plan view,

FIG. 3 shows an individual filament member in side elevation,

FIG. 4 shows an individual filament member viewed from above,

FIG. 5 is a plan view of a second embodiment of a member according tothe invention where the middle section of the member has been omitted,

FIG. 6 is a cross-section through the filament member along the lineVI--VI in FIG. 5,

FIG. 7 is a sectional view of the member, and

FIG. 8 is a top end view view through three juxtaposed filament members.

A further description of the design and mode of operation of an aircushion vehicle can be found in the description of the two abovementioned USA-patents.

FIG. 1 shows in sectional view a skirt section according to theinvention. A rather large number of filament members 1 are mounted in aguide profile 2 having an upwards extending mounting flange 3 which bymeans of fastening means, such as bolts, not shown, is fastened to thesidewall 4 of the vehicle hull. The guide profile 2 with the filamentmembers is mounted directly beneath the bottom of the hull 5 andpreferably in such a manner that the skirt downwards is angled slightlyinwards towards the middle of the air cushion chamber, because theangling of the skirt contributes to preventing air leakage from the aircushion chamber positioned to the right of the skirt shown in FIG. 1.

Each member 1 has a base portion 6 with engagement means in the form oftwo grooves facing in the transverse direction of the skirt forreceiving inwards bent projections 8 at the lower end of the guideprofile. It appears directly that the members in a simple manner may beinserted onto the projections 8 until the guide profile is filled upwith the filament members abutting against each other.

From the base portion 6 five elongated filaments 9 extend in thedownwards direction which filaments are transversely separated byinterspaces 10. The filaments are elongated stands or rods which in thetransverse direction taper downwards so that they have lesscross-sectional area in increasing distance from the base portion. Thusa suitable stiffness against transverse deflection in the upper sectionof the filament is combined with the desired flexibility for preventingice formations.

As will appear from FIG. 3 the filaments have by and large an eventhickness along the length of the skirt member. The filaments may,however, also taper in the length direction of the skirt, the filamentsmay e.g. be conical, but preferably they are designed as shown, whichprovides for a good barrier effect against air leakage from the aircushion chamber.

Two grooves 11 are made so in the one lateral face of the base portionthat they create a flow passage between the associated interspaces 10and a chamber 12 positioned in the guide profile 2 above the baseportion, when the members are mounted in the profile. A not shownconnecting piece for supply of de-icing fluid is mounted in the guideprofile, so that the piece debouch in chamber 12. The piece is connectedwith a supply pipe for de-icing fluid and by means of a valve the fluidmay be admitted according to need. Naturally it is possible to providethe guide profile with connection pipes for both hot gas and de-icingliquid such as propyl alcohol. Normally it is only necessary to supplypropyl alcohol immediately before initiation of the navigation orimmediately after termination of navigation thereby preventing icing ofthe skirt during standstill of the vehicle.

If the exhaust gas of the main engine is used as an de-icing fluid thereshould be a fan for suction of the exhaust gas, so that the engine isspared from operating against an excess pressure in the exhaust system.

When the de-icing fluid is admitted to chamber 12, as a consequence ofthe relatively large volume above the base portion of the skirt members,the fluid disperses itself evenly along the chamber in the guideprofile, wherefrom the fluid penetrates through grooves 11 and intointerspace 10 between the filaments.

Due to the fact that the filaments substantially abut against each otherthe de-icing fluid may penetrate down to the lower end of the filamentsand protect these against ice-formations.

It is obvious, that the filament member 1 may have a larger or lessnumber of juxtaposed filaments. The number of filaments and the lengthof these are adjusted to the size of the vehicle and to the desired airpressure in the air cushion chamber.

The brush member may in a simple manner be manufactured as an injectionmoulded plastic member.

In the same manner as described above the second embodiment of thefilament member 101 according to the invention has a base portion 106with engagement means in the form of two grooves 107 facing in thetransverse direction of the skirt. A central filament 113 and two outerfilaments 109 extend in the downwards direction from the base portion106. Two grooves 111 in the base portion set the interspaces 110 betweenthe central and the two outer filaments in flow communication with thearea situated above the base portion 106.

As best shown in FIGS. 6 and 8 each of the outer filaments has Z-shapedcross-section, where a forwards, in the longitudinal direction of theskirt, protruding web 115 at the outer side of the filament memberextends from a middle portion 114 having a comparatively largecross-sectional area and a backwards directed web 116 extends from thediagonally opposite side of the middle portion. The forwards projectingweb of one filament member overlaps the backwards facing web of theadjacent member so that the filament members may seize each other in thetransverse direction of the skirt.

The central filaments 113 have an oblong, mainly plane shape and arepositioned very closely to each other and form a wall blocking the airflow, when the filament members are in the mounted position.

I claim:
 1. A skirt for an air cushion vehicle having a number of aircushion chambers which are horizontally, outwardly delimited by theskirt in its transverse direction, which skirt extends in a longitudinaldirection, said skirt comprising: elongated filament members extendingdownwardly, each filament member having an upper base portion withengagement means for attaching the filament member to a retaineradjacent another filament member in said longitudinal direction of theskirt, said filament member including at least three elongated filamentsextending from the base portion and having a taper in cross-sectionalarea towards a free end of said filament, said at least three filamentsbeing juxtaposed in said transverse direction of the skirt to include aninner filament and an outer filament and a central filament, said innerand outer filaments having a substantially larger dimension in saidtransverse direction of the skirt than said central filament, and atleast one of said juxtaposed elongated filaments having at least one webthat protrudes in said longitudinal direction of the skirt and projectsover a portion of the adjacent filament member.
 2. A skirt according toclaim 1, wherein the thickness of said filament member in saidlongitudinal direction of the skirt is substantially even from said baseportion to said free end of said filaments, and the width of saidfilaments, in said transverse direction of the skirt, diminishes towardsthe free end of said filaments.
 3. A skirt according to claim 1, whereinsaid filament with said at least one web in cross-sectional view isZ-shaped with two webs projecting in said longitudinal direction of theskirt.
 4. A skirt according to claim 3, wherein said inner and saidouter filament have a Z-shaped cross-section, and said central filamenthas a cross-section being elongated in said longitudinal direction ofthe skirt.
 5. A skirt according to claim 1, wherein two of saidfilaments of said filament member are separated in said transversedirection of the skirt by a predetermined distance, and said baseportion of said filament member includes an upper side and at least oneflow passage for admission of de-icing fluid, the flow passage extendingfrom said upper side to the separation in said two filaments.